1. Technical Field
The present invention relates to automotive vehicle occupant restraint belt systems, and specifically to a control method for a four-point occupant restraint belt system to protect a seat occupant during a side impact collision and subsequent vehicle rollover.
2. Background Art
Automotive vehicles are usually equipped with occupant restraint belt systems for securing an occupant of the vehicle in his/her seat during a collision or the like. Some passenger vehicle occupant safety systems employ a four-point belt consisting of a lap belt extending across the seat occupant's lap and anchored to the seat and/or vehicle at both its ends, and a pair of shoulder belts. The left and right shoulder belts are commonly anchored to the seat at points adjacent each of the seat occupant's shoulders, extend downwardly over the torso, and are secured to the lap belt by one or more releasable latches.
The upper end of the shoulder belts may be wound around spools that allow the belts to extend and retract as necessary for comfort, convenience, and safety. It has been proposed to equip the spools with devices such as locks, spring- or motor-operated retractors, load limiters, and pre-tensioners. Examples of such devices and systems are described in U.S. Pat. Nos. 6,773,075; 6,375,270; and 7,625,048.
In most crash scenarios it is considered most safe to lock or tighten both the left and right shoulder belts in response to (or in preparation for) a vehicle impact, so as to keep the occupant securely restrained in the seat. This locking or tightening may be accomplished by locks, retractors, and/or pre-tensioners, and may be triggered by various impact and/or pre-impact sensors.
Some research has indicated, however, that in some side-impact collisions occupant safety can be improved if the shoulder belt on the side of the occupant's body that is away from the received impact is not locked or tightened, but rather is loosened so that the occupants torso may move in the direction in which the impact is directed. In a crash where the left side of the vehicle is struck, for example, the right shoulder belt should be loosened to permit the occupant's torso to move to the right.
In a real-world crash scenario, however, it is possible for a side impact to be immediately followed by a vehicle rollover. During a rollover, it is most likely that optimum safety is achieved by having both of the shoulder belts tightened.